1. Field of the Invention
The present invention relates to a liquid crystal display technology, and more particularly, to the improvement of an ejection head for ejecting alignment film forming composition.
2. Description of the Prior Art
A liquid crystal display (LCD) includes two glass substrates and a liquid crystal layer disposed between the glass substrates. At present, the LCD mainly refers to a thin film transistor (TFT) LCD. Basically, it takes three processes to produce the TFT LCD: to form patterns on the glass substrates, to seal liquid crystal between the glass substrates to form a liquid crystal cell, and to assemble a liquid crystal module (LCM). To cost down and to make products diverse, more than one liquid crystal cell is used on the glass substrates; instead, multiple liquid crystal cells are horizontally arranged on the glass substrates. The number of the liquid crystal cells and the position of the liquid crystal cells on the glass substrates are different depending on the model and the size of an individual product. After the liquid crystal is sealed, multiple liquid crystal cells on the glass substrates are cut to form a single liquid crystal display cell.
Liquid display units are formed after liquid crystal is sealed between the two glass substrates. In the process of producing liquid display units, an alignment film is disposed on each liquid display unit zone (short for display zone; other zones except for the display zone being called non-display zones). The alignment film disposed on the display zone of the glass substrate is equipped with alignment after being rubbed or being illuminated. In this way, the alignment film can affect the liquid crystal layer; that is, the liquid crystal is uniformly arranged in a fixed direction.
The formation of the alignment film comprises steps of (1) coating: alignment film forming composition is formed on the surface of a substrate through printing; the alignment film forming composition has been diluted with a solvent; (2) drying: the solvent is evaporated at about 100 degrees, and an alignment film which is equally distributed is formed; (3) baked: the alignment film is solidified at more than 180 degrees. In the step of coating, a roller coater is usually used. A PI (polyimide film) inkjet printing is also used.
The operating status of the inkjet printing is shown in FIG. 1. The alignment film forming composition is stored on the ejection head 110 and is sprayed out via a large number of fine nozzles 120 disposed on the ejection head 110. A glass substrate 130 is disposed on the print base 140. The alignment film forming composition sprayed via the nozzles 120 will fall on the glass substrate 130 and form uniform alignment droplets after the print base 140 moves or the ejection head 110 moves automatically. The alignment droplets will condense and become an alignment film after the alignment droplets spread on their own. A plurality of ejection heads 110 are used to cover the glass substrate 130 completely. The plurality of ejection heads 110 are controlled to spray the alignment film forming composition or to not spray the alignment film forming composition to decide where to be coated on the glass substrate 130.
The structure of the conventional nozzle 120 is shown in FIG. 2. The nozzle 120 comprises a chamber 121 and a composition source 126.
A liquid transportation pipe 124 and a pusher 122 are disposed on the bottom of the chamber 121 and the top of the chamber 121, respectively. The liquid transportation pipe 124 and the pusher 122 correspond with each other. The pusher 122 is used to push the alignment film forming composition out of the liquid transportation pipe 124.
Further, an inner annular groove 123 is disposed around the liquid transportation pipe 124 in the chamber 121. The inner annular groove 123 is connected to a liquid supply pipe 125 and is used to temporarily preserve the alignment film forming composition providing by the composition source 126. A bulge 127 is disposed between the inner annular groove 123 and the liquid transportation pipe 124 and is used to restrict flow direction of the alignment film forming composition flowing from the liquid supply pipe 125.
The composition source 126 is connected to the liquid supply pipe 125 disposed on the chamber 121 and is used to transport the alignment film forming composition to the chamber 121.
The use of the inkjet printing requires cooperation of its related technology. The alignment film forming composition tends to be spread unevenly once the droplets are larger. The larger droplets may damage the glass substrate, resulting drop mura, etc., so the nozzle is required to be as small as possible. In the production process of the alignment film, the operation time of the nozzle takes less than 30 percent of the total production time. In other words, the nozzle stays in an idle state for most of time, waiting for adjustment and operation of the equipment, input and output of raw material, etc. The spraying does not take much time in reality.
Because the idle time is long and the exit of the nozzle is small, the alignment film forming composition has to stay in the nozzle for a longer time. Some problems easily occur. Take one possible problem for example. The alignment film forming composition compries high polymers which has stickiness and solid content (the solid content of the liquid crystal is about 3-8% in general). The longer the alignment film forming composition stays on the nozzle, the easier the high polymers condense because the liquid solvent volatilizes easily and form large droplets. This will affect the quality of the alignment film. If the large droplets are not sprayed out for a long time, the condensed high polymers will even block the exit of the nozzle, causing the alignment film forming composition to not flow out normally.
It is urgent to solve the problems mentioned above such as how to improve the conventional nozzle, how to control the output timing of alignment film forming composition effectively, how to prevent high polymer alignment from condensing, and even how to avoid the nozzle from being blocked off.